Solvent based coating compositions useful as original equipment coatings and refinish coatings for automobiles and trucks that are composed of an acrylic polymer and an organic polyisocyanate crosslinking agent provide coatings of excellent quality and are well known in the art. One problem with such coating compositions has been the relatively high VOC content of these compositions. In an effort to reduce VOC, low molecular weight polymers have been used but these polymers increase the drying time of the composition as it cures. During curing a high molecular weight film is formed. Longer drying times reduce productivity in auto refinish shops by requiring the auto or truck to remain for a longer period of time in the area in which it was sprayed. A short rapid cure is desirable which leaves the coating in a tack free state and allows the auto or truck to be moved to another location to fully cure the coating usually under ambient temperature condition.
Attempts have been made to decrease the curing time of these coating compositions by using more reactive components or catalysts. However, while these decrease curing time since components of the coating composition are more reactive, they usually reduce the "pot life" of the coating composition as well. In the most extreme case, instant gellation of the composition occurs when, for example, the polyisocyanate is added to a polymer having reactive amine groups.
By "pot life" is meant the amount of time the viscosity of the composition remains at a sufficiently low level to be applied by conventional techniques which is usually done by spraying.
It would be desirable to have a coating composition that would cure rapidly after application to a "touch" dry state, i.e., dust and dirt does not stick and the finish is dry to the touch and have a pot life of several hours which would make the coating composition useful in an auto refinish operation or in a production facility such as an auto or truck manufacturing plant. The coating composition of this invention uses a polymer with reactive amine groups that when blended with a polyisocyanate does not gel but has an acceptable pot life but does cure rapidly to a touch dry state in a short time and cures to form a film with excellent properties such as high hardness, excellent mar and scratch resistance and excellent long term weathering properties.